A disk array apparatus is provided as a system for realizing, for example, reducing the risk of losing all data by storing user data in a storage area which is provided by a storage device such as a hard disk drive (HDD). The disk array apparatus has a controller which controls storing data, and storage devices connected thereto. The controller controls storing data in a storage area based on the instruction from a host. Also, the disk array apparatus performs RAID control employing a plurality of storage devices, and various types of control such as data replication and backup.
Meanwhile, a SAS is provided as an interface between a computer and storage devices. The SAS system has a computer as a device for performing data transfer which serves as a transfer source, an end device such as storage devices which serve as transfer destination (target), and an expander device which relays the data transfer between the end devices. A number of end devices can be connected to the expander device. A predetermined data-transfer speed (rate) is ensured at the physical links between the physical ports provided at each device. In the connection and the data path between the end devices via the expander device, data transfer is performed at the connection rate which is determined at the plurality of physical links by rate matching or the like.
In a SAS system, there performed a process for inserting ALIGN primitive to the transfer data in order to, for example, perform the rate matching in a connection including physical links of different rates. The ALIGN insertion in a SAS is described in a non patent document: Working Draft American National Standard, Project T10/1562-D Revision 5, “Information technology-Serial Attached SCSI (SAS)”, 4.3.2 Transmit data path, pp. 45-49, 7.2.5.2 ALIGN, pp. 152-153, 7.13 Rate matching, pp. 191-193, (online), Jul. 9, 2003, (searched on Jul. 22, 2004), the Internet <URL: http://www.t10.org/drafts.htm/sas-r05.pdf>.